Blood is a connective liquid tissue that is present in man and the majority of evolved animals. Despite an identical cellular composition, there is a variability of various elements of the blood, defined by different antigenic systems called blood groups.
In practice, the focus more particularly is on erythrocyte blood groups, antigen systems that are located on the surface of red blood cells, such as, for example, the ABO, rhesus, Kell, Duffy, MNS, and Lewis systems, etc.
Conventionally, the determination of a blood group is done on antigen-antibody recognition. When a specific antibody of the antigen recognizes the latter, it is fixed. Generally, the antibodies that are used in the recognition of the blood groups are IgM immunoglobulins that clump the red blood cells. The conventionally used techniques consist in seeking and identifying the presence or absence of antigens of the blood group on the surface of the erythrocytes or in seeking and identifying the presence or the absence of anti-antigenic antibodies of the blood group in the plasma.
In particular, for the ABO system, the Beth Vincent test makes it possible to determine the antigens that are borne by the red blood cells, and the complementary Simonin-Michon test or serum-check test makes it possible to determine the antibodies that circulate in the serum.
In the Beth Vincent test, the red blood cells of the individual, obtained after phase separation of the cells and the plasma, either by centrifuging or by decanting, are brought into the presence of antibody reagents of a known specificity. Generally, this test is made visible by observation of clumping red blood cells when the antibodies recognize the corresponding erythrocyte antigens.
In the Simonin test, the plasma of the individual is brought into the presence of test red blood cells that each belong to a specific antigen group of the ABO system. It involves a test for clumping the plasma of the individual with test erythrocytes.
For the research of so-called irregular antibodies or RAI, detecting the presence or the absence of immunoglobulins directed against various erythrocyte antigens of the individual in the blood of an individual is involved. For this purpose, an attempt is made to demonstrate the attachment of these immunoglobulins to test red blood cells whose antigens are known, with the direct and indirect Coombs technique, whereby the comparison of the results makes it possible to deduce the presence or the absence of immunoglobulins.
There are a large number of processes and devices used for phenotyping in the field of immunology-hematology, whereby the techniques can be manual, on an opaline plate, in a microplate tube or cup, or else completely automated using a robot for distributing samples and reagent, stirring, incubating and automatic reading. Two reference techniques in particular are known: the microplate techniques and the test gel filtration techniques.
However, these existing techniques for phenotyping blood groups have numerous drawbacks.
The microplate techniques, for example, require a stirring phase that is critical because the simultaneously present multiple reactions on the substrate do not have the same resuspension kinetics. They should be produced under visual monitoring, and it is necessary to be particularly attentive to the adhesion phenomena of certain reagents.
Likewise, during the implementation of test gel filtration techniques, there is also a risk of not detecting certain agglutinations, in particular during the plasmatic test of the ABO group. Another drawback is the too-frequent detection of autoantibodies in relation to the test erythrocyte preparations, in particular those that are treated by proteolytic enzymes.
In addition, all of these techniques have a major drawback because they require a preliminary centrifuging of the whole blood so as to separate the constituent elements of the blood, a restrictive stage that greatly increases the time and the cost of analysis and that requires the use of centrifuges that are bulky and difficult to handle.
So as to eliminate this heavy centrifuging stage, variants have been developed, based on the use of magnetic particles.
By way of example, it is possible to cite the patent application EP-0,351,857 that describes a process for immunological metering that uses magnetized markers such as antibodies or antigens that are fixed to the magnetic latex balls. In particular, an RAI technique by immunoadhesion is described in which a magnetic field is applied to erythrocytes that are previously fixed to the bottom of a microplate cup, sensitized with the serum to be tested, washed and mixed with magnetic latex balls that are coated with an anti-immunoglobulin. The application EP 0,230,768 that describes a process for co-aggregation of magnetic particles that are able to link to a substance that is contained in a sample by means of polycationic compounds in the presence of a magnetic field is also known.
However, these different techniques also have numerous drawbacks. They are difficult and take a long time to implement, are not very economical, and require the use of devices that are complex and not very mobile.